Not going to read through the whole thread, but we've all experienced non paying buyers whether through ebay, here, etc. I don't think there's any way to avoid it because it can and does happen.
Recently, I've had a buyer on ebay who made an offer for a $3000 item which I accepted. After a few days of waiting and a few messages to the buyer about the payment, I never received a message back from him at all. I decided to cancel the transaction to get my $ back on fees because I don't want to waste my time with it.
If you are listing something on eBay and want a guaranteed payment to prevent bidders/buyers from not paying, then do a buy it now auction. Set your price, and click on immediate payment through PayPal required. That way, the buyer cannot buy the item without paying right away and you don't have to worry about whether or not the buyer will pay. It's worked out well for me after having multiple non paying buyers in the past.